Have you noticed how the power of suggestion can affect people? I recently taught a class and the someone told the class that no one does well on one of the test- guess what, no one did well on the test.
In a subject that I used to teach I showed movies that were on the science side of infant behavior. If I told the class that the movie was dry but pick out the important points they would comment that the movies weren't good, but if I got excited and said watch what the newborn/ infant can do I would receive comments how great the movies were.
I actually co-taught with someone else and she told one of the students he would never make it and would fail the tests, of course he failed the test. Go figure.